In recent years, there has been a growing demand for transmission of multimedia data with a low delay while performing media reference signal synchronization (so-called “GENLOCK synchronization”) via the internet, a local area, network (LAN), or other transmission line.
For example, there is a system in which a camera and its control unit (so-called “camera control unit” (CCU)) are connected with a high definition serial digital interface (HD-SDI) cable and uncompressed synchronization transmission is performed in a broadcasting station. In recent years, the HD-SDI cable of this system has been replaced with an Ethernet (trademark) cable and the transmission has been performed on the Ethernet (trademark) while performing GENLOCK synchronization with an IP packet.
For such a purpose, when IP transmission of multimedia data is performed, the usability is required, which is equivalent to that of the transmission via the HD-SDI cable. Therefore, highly accurate GENLOCK synchronization and low delay transmission equal to or less than a video frame interval are required.
In response to the request, a system is proposed in which every several numbers of lines of each picture of a moving image is encoded as one encoding block (a line block) by wavelet transformation (for example, see Patent Document 1).
In this system, the encoding is started without waiting an input of all of data in a picture. Therefore, when generated, encoded data is transmitted via a network and is decoded at a reception side, a decoding process can be started before receiving all of the data in the picture. That is, if a network propagation delay is substantially small, real time (instantaneous) moving image transmission with a delay equal to or less than the frame interval becomes possible.
In such data transmission, it is necessary for a reception device to buffer (temporarily hold) received data in order to deal with a delay in an encoding process, in a data transmission process, in a QoS control process, and the like. In other words, setting of the encoding process, the QoS control process, and the like is performed (not to overflow) in accordance with a buffer time at a receiving side. That is, image quality of decoded image or transmission quality depends on the buffer time.
By the way, in a conventional system, when data is transmitted by this data transmission from a plurality of transmission devices to one reception device, reception buffer times with respect to the transmission devices are set independently of each other, or, are set to be a predetermined time (a common reception buffer time is used).